Multiple hearth furnace

Abstract

A multiple hearth furnace including a rabble arm with a tubular structure and a solid plug body. The latter is received in a socket arranged in an arm fixing node. It has an axial through boring and cooling fluid supply and return channels arranged around this through boring. A clamping bolt is rotatably fitted in the through boring. It has a bolt head, which can be brought by rotation into and out of hooking engagement with an abutment surface on the arm fixing node. A threaded end of the clamping bolt sticks out of the through boring at the rear end of the plug body. A threaded sleeve, which is screwed onto this threaded end, bears on an abutment surface at the rear end of the plug body for exerting a clamping force onto the clamping bolt.

1. A multiple hearth furnace comprising:
 a vertical rotary hollow shaft including at least one rabble arm fixing node; 
 at least one rabble arm including a tubular structure for circulating therethrough a cooling fluid and a coupling end that is received like a plug in a socket arranged in said arm fixing node, said coupling end including cooling fluid supply and return means therein; and 
 securing means for securing said rabble arm with its coupling end in said socket, said securing means including: 
 a clamping bolt for pressing said coupling end into said socket, said clamping bolt protruding out of the coupling end of said rabble arm where it has a bolt head that can be brought by rotation of said clamping bolt about its central axis into and out of hooking engagement with an abutment surface on said arm fixing node; and 
 a threaded sleeve screwed onto a threaded end of said clamping bolt for exerting a clamping force onto said clamping bolt; wherein: 
 said coupling end has a through boring in which said clamping bolt is rotatably fitted so that its threaded end sticks out of said through boring; and 
 said threaded sleeve, which is screwed onto said threaded end, bears on an abutment surface of said coupling end for exerting said clamping force onto said clamping bolt; 
 wherein said coupling end is formed by a solid plug body which has a front end and a rear end; 
 wherein said tubular structure of said rabble arm comprises an arm support tube, which is connected to the rear end of said plug body, and a gas guiding tube, which is arranged inside said arm support tube and cooperates with the latter to define between them a small annular cooling gap for channeling the cooling gas from the shaft to the free end of the rabble arm, and the interior section of said gas guiding tube forms a return channel for the cooling gas; 
 wherein said cooling fluid supply and return means include at least one cooling fluid supply channel and at least one cooling fluid return channel arranged in said solid plug body around said through boring, wherein at said rear end of said solid plug body, said at least one cooling fluid supply channel is in communication with said small annular cooling gap and said at least one cooling fluid return channel is in communication with said return channel; and 
 said through boring, in which said clamping bolt is rotatably fitted, axially extends through said solid plug body, and said abutment surface, onto which said threaded sleeve bears, is formed on the rear end of said solid plug body. 
 
     
     
       2. The furnace as claimed in  claim 1  wherein said securing means further comprises:
 a positioning tube secured with a first end to said clamping bolt and extending through the entire rabble arm up to the free end of the latter. 
 
     
     
       3. The furnace as claimed in  claim 1  wherein said securing means further comprises:
 an actuation tube secured with a first end to said threaded sleeve and extending through the entire rabble arm up to the free end of the latter, where its second end supports a coupling head for coupling thereto an actuation key for transmitting a torque to the threaded sleeve via said actuation tube. 
 
     
     
       4. The furnace as claimed in  claim 3 , wherein said securing means further comprises:
 a positioning tube secured with a first end to said clamping bolt and extending through the entire rabble arm up to the free end of the latter, wherein said positioning tube is co-axial to and rotatably supported within said actuation tube. 
 
     
     
       5. The furnace as claimed in  claim 3 , wherein:
 one end of said arm support tube is connected to said plug body and the other end is closed by an end-cup; and 
 said actuation tube axially extends through said gas guiding tube and its free end is rotatably supported in a sealed manner in a through hole of said end-cup. 
 
     
     
       6. The furnace as claimed in  claim 1 , wherein:
 said solid plug body is a solid cast body; and 
 said through boring, in which the cylindrical shank portion is rotatably fitted, said at least one cooling fluid supply channel and said at least one cooling fluid return channel are provided as bores in said solid cast body. 
 
     
     
       7. The furnace as claimed in  claim 1 , wherein:
 said socket has therein a first concave conical seat surface located in proximity of its bottom surface and a concave cylindrical guiding surface located closer to the entrance opening of said socket; 
 said plug body has thereon a first convex conical counter-seat surface and a convex cylindrical guiding surface, cooperating with said first concave conical seat surface, respectively said concave cylindrical guiding surface in said socket. 
 
     
     
       8. The furnace as claimed in  claim 7 , wherein:
 said socket has therein a second concave conical seat surface, said concave cylindrical guiding surface lying between said first concave conical seat surface and said second concave conical seat surface; and 
 said plug body has thereon a second convex conical counter-seat surface, said convex cylindrical guiding surface lying between said first convex conical counter-seat surface and said second convex conical counter-seat surface. 
 
     
     
       9. The furnace as claimed in  claim 8 , wherein:
 all said conical surface are ring surfaces of a single cone. 
 
     
     
       10. The furnace as claimed in  claim 9 , wherein:
 said cone has a cone angle within the range of 10° to 30°, preferably within the range of 18° to 22°. 
 
     
     
       11. The furnace as claimed in  claim 8 , wherein:
 at least one cooling gas channel is arranged in said rabble arm fixing node that has an opening in said concave cylindrical guiding surface; and 
 at least one cooling gas channel is arranged in said plug body of said rabble arm that has an opening in said convex cylindrical guiding surface, wherein said openings are overlapping when said plug body is seated on its seats in said socket. 
 
     
     
       12. The furnace as claimed in  claim 1  wherein:
 said rabble arm fixing node comprises a ring-shaped cast body made of refractory steel, 
 said sockets being radially arranged in said ring-shaped cast body. 
 
     
     
       13. The furnace as claimed in  claim 12 , wherein:
 said shaft includes a support structure consisting of said rabble arm fixing nodes and of intermediate support tubes that are interposed as structural load carrying members between said rabble arm fixing nodes. 
 
     
     
       14. The furnace as claimed in  claim 13 , wherein:
 said rabble arm fixing nodes and said intermediate support tubes are assembled by welding. 
 
     
     
       15. The furnace as claimed in  claim 1  wherein at least one section of said shaft extending between two adjacent hearth chambers comprises:
 a intermediate support tube fixed between two arm fixing nodes to form an outer shell; 
 an intermediate gas guiding jacket arranged within said intermediate support tube so as to delimit an annular main cooling gas supply channel between both; and 
 an inner gas guiding jacket arranged within said intermediate support tube so as to delimit annular main cooling gas distribution channel between both, said inner gas guiding jacket further defining the outer wall of a central exhaust channel. 
 
     
     
       16. The furnace as claimed in  claim 15 , wherein said arm fixing node comprises a ring-shaped cast body including:
 at least one of said sockets for receiving therein said plug body of said rabble arm; 
 a central passage forming said central exhaust channel for the cooling gas within said arm fixing node; 
 first secondary passages arranged in a first ring section of said cast body, so as to provide gas passages for cooling gas flowing through said annular main cooling gas distribution channel; 
 second secondary passages arranged in a second ring section of said cast body, so as to provide gas passages for cooling gas flowing through said annular main cooling gas supply channel; 
 a first channel means arranged in said cast body, so as to interconnect said annular main cooling gas supply channel with a gas outlet opening within said at least one socket; and 
 a second channel means arranged in said cast body, so as to interconnect a gas inlet opening within said at least one socket with said central passage. 
 
     
     
       17. The furnace as claimed in  claim 16 , wherein:
 said second channel means comprises a through hole in axial extension of said socket. 
 
     
     
       18. The furnace as claimed in  claim 16 , wherein:
 said first channel means comprises at least one oblique bore extending through said ring-shaped cast body from said second ring section into a lateral surface delimiting said socket. 
 
     
     
       19. The furnace as claimed in  claim 1  wherein:
 said arm support tube is a thick walled stainless steel tube extending over the whole length of the rabble arm and welded with one end to a shoulder surface on the rear side of the plug body. 
 
     
     
       20. The furnace as claimed in  claim 1  wherein said rabble arm further comprises:
 a micro porous thermal insulation layer arranged on said arm support tube; and 
 a metallic protecting jacket covering said micro porous thermal insulation layer. 
 
     
     
       21. The furnace as claimed in  claim 20 , wherein said rabble arm further comprises:
 metallic rabble teeth fixed to said metallic protecting jacket by welding; 
 and anti-rotation means arranged between said arm support tube and said metallic protecting jacket.